Ammon News - By MARK LANDLER and JONATHAN WEISMAN/ The New York Times

WASHINGTON — Each morning for the last week, at 7:45, more than a dozen White House aides have mustered in the corner office of President Obama’s chief of staff, Denis R. McDonough, to get their marching orders for what has become the most intense, uphill lobbying campaign of the Obama presidency.

The White House’s goal is to persuade Congress to authorize a limited military strike against Syria to punish it for a deadly chemical weapons attack. But after a frenetic week of wall-to-wall intelligence briefings, dozens of phone calls and hours of hearings with senior members of Mr. Obama’s war council, more and more lawmakers, Republican and Democrat, are lining up to vote against the president.

Officials are guardedly optimistic about the Senate, but the blows keep coming. On Saturday, Senator Mark Pryor, Democrat of Arkansas, perhaps the most endangered incumbent up for re-election, came out against the authorization to use force.

In the House, the number of rank-and-file members who have declared that they will oppose or are leaning against military action is approaching 218, the point of no return for the White House. Getting them to reverse their positions will be extremely difficult.

Administration officials say publicly that they are not rattled by such grim vote counts. The debate, they say, will only be fully engaged this week, when Congress returns from recess and Mr. Obama is back from his trip to Sweden and Russia. On Tuesday night, he will lay out his case for a strike to the nation in a speech from the White House.

“It’s too early to jump to any conclusions on where the House or Senate is,” Mr. McDonough said in an interview on Friday. “The effort will only intensify next week.”

To improve its odds, the White House is enlisting virtually every senior official from the president on down. In addition to members of Congress, it is reaching out to Jewish groups, Arab-Americans, left-leaning think tanks and even officials from the George W. Bush administration, some of whom are acting as surrogates. It is also getting help from the nation’s most powerful pro-Israel group, the American Israel Public Affairs Committee, which is mounting its own campaign for military action.

The White House and its allies in Congress differ on how the administration handled the first week of the campaign. Administration officials said they succeeded in dispelling doubts about whether the forces of the Syrian president, Bashar al-Assad, carried out the chemical weapons attack on the outskirts of Damascus on Aug. 21 that they say left more than 1,400 people dead.

“We set a goal this week of making sure people understood the facts of the case,” Mr. McDonough said Friday. “No one with whom I’ve spoken doubts the intelligence. We’re not really debating the veracity of the central charge.”

But people on Capitol Hill said the White House’s initial case for action proved unpersuasive, particularly in the hearings with Secretary of State John Kerry, Defense Secretary Chuck Hagel and the chairman of the Joint Chiefs of Staff, Gen. Martin E. Dempsey.

Lawmakers came away believing that General Dempsey projected an image of military reluctance, that Mr. Hagel seemed occasionally unsure of himself, and that Mr. Kerry exuded a characteristic air of confidence that some members appreciated and others chafed at.

Aides to Congressional Democratic leaders said Saturday that videos of the aftermath of the chemical weapons attack outside Damascus, showing civilians lying on the ground in convulsions, have been shown to lawmakers in classified briefings open only to members of Congress. Senator Dianne Feinstein of California, the chairwoman of the Senate Intelligence Committee, posted the videos on the committee’s Web site on Saturday for the public to see.

The next phase of the campaign will be more individualized, and more from Mr. Obama himself. Democrats who are balking are being asked at least to vote against Republican procedural moves meant to delay or derail an up-or-down vote. After all the arguments are exhausted, aides said, it will come down to a personal pitch: the president needs you to save him from a debilitating public defeat.

But first, advisers said, the president needs to explain to the public in his speech on Tuesday why Syria is not another Iraq.

“Right now, to most of the country, this seems like a simple question of, ‘Is Congress going to vote to start another war?’ ” said David Plouffe, a former senior adviser to Mr. Obama who, like other veterans of his 2008 campaign, was back in the West Wing last week. “Tuesday night and other opportunities can help fill in the picture for people about both the rationale and limited nature of the response.”

On the day the president is speaking, the American Israel Public Affairs Committee plans to blanket Capitol Hill with 250 advocates, having already contacted dozens of lawmakers to urge them to support a strike.

The advocates will carry a simple message, according to a person involved in the effort: Syria is a proxy for Iran, and the failure to enforce Mr. Obama’s “red line” against the use of chemical weapons by Mr. Assad will be interpreted in Tehran as a sign that he will not enforce a red line against the production of nuclear weapons by the Iranian government.

Israel itself is staying out of what it regards as a domestic American political debate. But Michael B. Oren, the Israeli ambassador to the United States, said he was telling any lawmaker who expressed fears that Syria would attack Israel in retaliation for an American missile strike: “Don’t worry about us. We can defend ourselves.”

Among the most visible surrogates could be Hillary Rodham Clinton, Mr. Obama’s former secretary of state, who aides say is likely to address Syria at one or both of two events this week: a previously scheduled visit to the White House on Monday to promote wildlife conservation, and a speech the next day in Philadelphia.

The White House is also putting officials, including the president, before audiences and television cameras. Mr. Obama will tape interviews on Monday with ABC, CBS, NBC, Fox, PBS and CNN. Mr. McDonough will appear on all five Sunday news programs, and on Monday the national security adviser, Susan E. Rice, will address the New America Foundation, a nonpartisan public policy institute.

The last time the White House lobbied this intensively on a single issue was the 2009 health care law. But unlike that battle, which was largely pitched to the Democratic ranks, the White House this time is also appealing to Republicans. Administration officials note that in private conversations, lawmakers repeatedly asked to have their voices heard on Syria.

The administration’s shift began taking shape late last week at briefings for Congressional chiefs of staff and legislative directors. At a bipartisan briefing that was well attended, Robert S. Ford, the senior American envoy to the Syrian opposition, offered a frightening picture of a Middle East with uncontrolled weapons of mass destruction, aides who attended said.

Tailoring the pitch, the White House and Republican Congressional leaders organized another briefing just for Republican staff members to hear from Stephen Hadley, a former national security adviser to Mr. Bush, and Eric S. Edelman, a former top aide to Vice President Dick Cheney.

Mr. Edelman, in particular, focused on what Republican leaders have been emphasizing: a broader context for the Syrian conflict that includes Iran, loose weapons of mass destruction and the threat to Israel, according to Republican aides.

On the Democratic side, Mr. McDonough met with the Congressional Hispanic Caucus, while Ms. Rice met with the Congressional Black Caucus, whose loyalty might be crucial.

On Friday, Mr. McDonough and Representative Nancy Pelosi of California, the minority leader, held a conference call with Democratic freshmen. Some Democrats have been invited to the Situation Room to meet with Vice President Joseph R. Biden Jr.

Leaders in both parties say that there is a narrow window to win over or change enough votes to secure passage of the authorization, but that window may close before Mr. Obama’s speech.

Representative Eric Cantor of Virginia, the House majority leader, wrote an opinion article for The Richmond Times-Dispatch explaining his support for a strike in terms that could sway other Republicans — namely that it could combat the influence of Iran and Hezbollah.

But aides say there was a reason Mr. Cantor chose his hometown newspaper: He had to reach his own constituents, who, like most Americans, are opposed to military action.

Representative Jason Chaffetz, Republican of Utah, called on Mr. Cantor to hear his position but emerged leaning toward no. “I don’t see how they do that now,” he said of winning authorization. “They may be able to squeak it out. But at best it’s going to be razor thin.”